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Quarterback C.J. Beathard threw two interceptions and fumbled twice, including a decisive play in the fourth quarter that led to a Cardinals defensive touchdown. He was stripped by linebacker Haason Reddick, and Josh Bynes returned it 23 yards to put Arizona up 21-12.

That came after the 49ers appeared to have momentum back and a second home victory within their grasp. They scored a fourth-down touchdown to receiver Trent Taylor, cutting the lead to 2, and then forced a three-and-out from Arizona’s offense.

The ugly game was starting to turn.

But Reddick’s forced fumble took the air out of Levi’s Stadium, thwarting San Francisco’s comeback attempt, continuing the 49ers theme from throughout the 2018 season: Missing out on opportunities to win games.

“When you look at the stat sheet,” coach Kyle Shanahan said, “you double them in time of possession, yards. I thought our defense played their tail off, did good on third down. You look at those things, it’s hard to find how you lost the game. And then it’s very easy when you look at the turnover column.

“I haven’t been part of any game — I don’t think many people have — where five turnovers to zero leads to a win. We have to improve that drastically to have a chance.”

The 49ers’ banged up offensive line struggled to protect Beathard, who was sacked four times.

“He’s a quarterback and there’s a lot of responsibility on the quarterback to protect the ball,” Shanahan said. “There’s 10 other guys out there that can make it easier on him too. I’ll get through all of them. Usually, fumbles (are) hard to pin on the quarterback, but we’ll look at them hard tomorrow and coach him up the best we can on them.”

Chandler Jones, last season’s NFL sack leader, filled up the stat sheet with a sack, two quarterback hits, two tackles for loss, a pass break up, six tackles, a forced fumble and a fumble recovery.

The All-Pro was a thorn in the side of left tackle Joe Staley, who left last week’s game with a right knee injury. He didn’t practice until Friday and came in early the entire week to receive treatment.

“I’m frustrated, personally,” Staley said. “Got to play better. I had a bad game.”

San Francisco was on the edge of scoring territory during the first series of the third quarter following an ugly first half in which it either punted or turned the ball over on six consecutive possessions. Beathard went back to throw following play action and Jones beat Staley outside, knocking the ball out of Beathard’s hands and out-wrestling him for the recovery.

It killed whatever momentum the 49ers had coming out the locker room, even after Pierre Garçon helped the team convert an unlikely third-and-14 with a diving 20-yard reception.

“I got to anticipate the upfield rush there and not go so hard on selling the run,” Staley said. “He wasn’t biting on it.”

The 49ers entered the game without receivers Marquise Goodwin (quadriceps, hamstring) and rookie Dante Pettis (knee), who were the team’s top-two options at “X” receiver. That position is typically tasked with stretched defenses thin with downfield speed.

Instead, Shanahan was forced to rely on rookie seventh-round pick Richie James (one catch, seven yards) and former undrafted free agent Victor Bolden Jr. (one catch, 10 yards), playing in his first game back from a four-game suspension to open the season.

It led to San Francisco featuring a slew of screen passes to offset Arizona’s blitz-heavy game plan. The 49ers’ top two pass catchers were tight end George Kittle and fullback Kyle Juszczyk, who combined for 11 receptions and 158 yards.

“The more guys you have out there, the easier it is, so you try to balance it all out. You try to go where they’re not defending and when they defend that you try to go to the other spots,” Shanahan said. “The more guys go down, the harder it gets.”

Rookie quarterback Josh Rosen, making his first career road start, completed just 10 of 25 passes (40 percent) for 170 yards. Seventy-five came on the first play from scrimmage, when he found receiver Christian Kirk streaking wide open for a touchdown.

It was a loud response to San Francisco’s emphatic scoring drive to open the game, making it like look the 49ers were setting up to cruise to their first division win of the year.

Kirk broke free down the middle of the field because cornerback Ahkello Witherspoon was anticipating help on the inside from free safety Adrian Colbert. But Colbert, who sat out last week’s game with a hip injury, bit inside to cover Larry Fitzgerald, leaving Kirk open beyond San Francisco’s secondary.

“It was just an undisciplined play by me. I saw Larry flash and it was just a bad play on my part. It is something that I have to correct,” Colbert said.

Said Shanahan: “Usually in cover-three, you’ve got someone in the middle of the field.”

That completion accounted for 34 percent of the Cardinals’ offensive output. Their second touchdown came four plays after a Raheem Mostert fumble, who was in the game after starting running back Matt Breida sprained his left ankle late in the first quarter.

Breida left the game after getting off to a promising start, netting 56 yards on eight carries, which dropped his league-leading yards per carry to 7.5.

With Breida sidelined, San Francisco was forced to rely on Alfred Morris, who finished with just 61 yards on 18 carries and hasn’t been nearly as effective as Breida. Mostert averaged just 2.2 yards per carry, including his crucial first-half fumble.

The 49ers will have a long week to rehash the loss. Up next is a trip to play the Green Bay Packers on “Monday Night Football.”